Field of the Invention
The present invention relates to a ceramide dispersion composition.
Description of the Related Art
Ceramide is a major component of intercellular lipids in a horny cell layer existing among horny cells of skin. The intercellular lipids in a horny cell layer such as ceramide are layered to form a periodic structure (lamella structure) and fill the gaps among horny cells, thereby exhibiting the barrier function of skin.
In a lamella structure which is formed of intercellular lipids in a horny cell layer, there are two types of lamella structures, namely, a short periodic lamella structure (Short Periodicity Phase; hereinafter also referred to as “SPP”) having a layer thickness of approximately 6 nm, and a long periodic lamella structure (Long Periodicity Phase, hereinafter also referred to as “LPP”) having a layer thickness of approximately 13 nm. Especially, it is known that an LPP formed of a ceramide having an O-acyl moiety (also referred to as “acyl ceramide”) as an essential component greatly contributes to the barrier function of skin.
The amount of ceramide in skin decreases owing to aging or the like, whereby the barrier function of skin decreases. In addition, in the case of the skin of a patient suffering from atopic dermatitis, it is known that the amount of ceramide decreases not only in a lesional part but also in a non-lesional part. Accordingly, in recent years, various kinds of ceramide dispersion compositions have been developed in expectation of a skin care effect or the like of ceramide.
In order to sufficiently cause an effect such as a skin care effect expected to be exhibited by ceramide, it is necessary to enhance the skin penetration of ceramide. Taking the skin penetration of ceramide into consideration, it is desired that the particle diameter of dispersed particles including ceramide is small. However, it is difficult to micronize dispersed particles including, especially, a ceramide having an O-acyl moiety, because the ceramide has a large molecular weight and a hydrophobic structure, and the ceramide is easy to crystallize. In addition, even after dispersing a ceramide having an O-acyl moiety, it is difficult to prevent aggregation or the like to keep the dispersion stability.
Under such a background, International Publication WO 2015/136784 discloses a ceramide-containing composition which contains a specific ceramide having an O-acyl moiety and a nonionic surfactant, in which the average particle diameter of dispersed particles is less than 60 nm. The ceramide-containing composition disclosed in International Publication WO 2015/136784 has small fluctuation of the particle diameter of dispersed particles even in a case in which the ceramide-containing composition has been stored, for example, at 50° C. for 90 days, so that the dispersion stability under a high temperature condition is excellent.